1. Field of the Invention
The present invention relates to a substrate transport apparatus and method, which transports a substrate that has been exposed by a liquid immersion method, an exposure apparatus and method, and a device fabricating method.
2. Description of Related Art
Semiconductor devices and liquid crystal display devices are fabricated by a so-called photolithography technique, wherein a pattern formed on a mask is transferred onto a photosensitive substrate. An exposure apparatus used in this photolithographic process includes a mask stage that supports the mask, and a substrate stage that supports the substrate, and transfers the pattern of the mask onto the substrate via a projection optical system while successively moving the mask stage and the substrate stage. There has been demand in recent years for higher resolution projection optical systems in order to handle the much higher levels of integration of device patterns. The shorter the exposure wavelength used and the larger the numerical aperture of the projection optical system, the higher the resolution of the projection optical system. Consequently, the exposure wavelength used in exposure apparatuses has shortened year by year, and the numerical aperture of projection optical systems has increased. Furthermore, the mainstream exposure wavelength currently is the 248 nm KrF excimer laser, but an even shorter wavelength 193 nm ArF excimer laser is also being commercialized. In addition, as with resolution, the depth of focus (DOF) is important when performing an exposure. The following equations express the resolution R and the depth of focus δ, respectively.R=k1·λ/NA  (1)δ=±k2·λ/NA2  (2)
Therein, λ is the exposure wavelength, NA is the numerical aperture of the projection optical system, and k1 and k2 are the process coefficients. Equations (1) and (2) teach that if the exposure wavelength λ is shortened and the numerical aperture NA is increased in order to enhance the resolution R, then the depth of focus δ narrows.
If the depth of focus δ becomes excessively narrow, then it will become difficult to align the surface of the substrate with the image plane of the projection optical system, and there will be a risk of insufficient margin of focus during the exposure operation. Accordingly, a liquid immersion method has been proposed, as disclosed in, for example, PCT International Publication WO99/49504 below, as a method to substantially shorten the exposure wavelength and increase the depth of focus. This liquid immersion method fills a liquid, such as water or an organic solvent, between the lower surface of the projection optical system and the surface of the substrate, thus taking advantage of the fact that the wavelength of the exposure light in a liquid is 1/n that of in air (where n is the refractive index of the liquid, normally about 1.2-1.6), thereby improving the resolution as well as increasing the depth of focus by approximately n times.
Incidentally, a substrate transport member unloads the substrate, which was exposed by the liquid immersion method, from the substrate stage. At this time, if liquid has adhered to the rear surface of the substrate, then the liquid between the substrate transport member and the substrate forms a lubricating film, and the substrate becomes slippery (easily mispositioned) with respect to the substrate transport member, and there is a possibility of a problem arising wherein the substrate transport member will no longer be able to transport the substrate in the desired state. In addition, if liquid has adhered to the substrate transport member, then that liquid forms a film that causes the substrate to slip with respect to the substrate transport member, and there is consequently a risk that the substrate cannot be transported satisfactorily. If liquid has adhered to the substrate in the case where the substrate transport member holds the substrate by vacuum suction, then there is a possibility that a problem will arise wherein that liquid will infiltrate and damage the vacuum system.
In addition, if the transportation is executed in a state wherein liquid has adhered to the substrate and/or the substrate transport member, then problems arise, such as rusting of the various equipments and/or members in the vicinity of the transport pathway due to the liquid that falls from the substrate during transport, the inability to maintain the cleanliness level of the environment wherein the exposure apparatus is disposed, and the like. Alternatively, there is also the case wherein the fallen liquid can bring on environmental changes (humidity changes) in the vicinity of the exposure apparatus.
If liquid has adhered to the substrate transport member, then there is a possibility that that liquid will adhere to and contaminate the substrate, and, if the liquid that has adhered to the substrate dries before the exposure process, then a trace thereof will remain on the substrate surface, which can cause a deterioration of the quality of the device that is manufactured. In addition, there is a risk that, in a state wherein liquid has adhered to the substrate after the exposure process, for example, if the development process is executed, then it will cause uneven development and the like, and will also cause substrate contamination due to the liquid that has adhered to the substrate and that will collect impurities (dust and the like) present in the atmosphere, thus making it impossible to fabricate a device that has the desired performance.
The present invention is made considering these circumstances, and it is an object of the present invention to provide: a substrate transport apparatus and method, wherein a substrate exposed by the liquid immersion method can be satisfactorily transported in the desired state; an exposure apparatus and method; and a device fabricating method.